Apparatus for heating



Aug. 24, 1937.

1 WILSON APPARATUS FOR HEATING Filed July 31, 1935 2 Sheets-Sheet lINVENTOR Aug. 24, 1937. L, WILSON i 2,091,172v

APPARATUS FOR HEAT ING Filed July 51, 1935 2 Sheets-Sheet 2 INVENTORPatented Aug. 24, 1937 Uur/TED STATES PATENT OFFICE 2 Claims.

My invention relates broadly to the art of heating and, particularly, tothe heating of metallurgical furnaces, such as those for the heattreatment of Various materials, for example,

sheet steel.

Heating, normalizing, and annealing furnaces of the continuous or tunneltype have been used for a considerable period. In the so-called rollerhearth furnaces, the material is passed through an elongated heatingchamber on a roller conveyor and heated as it moves therethrough. Theearliest method of heating fuelfired furnaces of this type was toprovide burners extending through the side walls thereof, and supplythem with fuel for combustion within the heating chamber and in directcontact with the material passing therethrough. Several objections tothis method were experienced. In the rst place, the temperaturethroughout the furnace was not uniform but varied according to thedistance of the point under observation from the nearest burner. Thedirect contact of the combustion gases at considerable velocity, withthe material being treated, sometimes has a deleterious effect on thelatter. Where the combustion gases have direct contact with thematerial, furthermore, they constitute the atmosphere in which the heattreatment takes place and it is not possible to provide a. specialatmosphere which is desirable in some cases. In an attempt to overcomethe aforementioned disadvantages of the original method of direct firingcontinuous or tunnel type furnaces, it was proposed to place the burnersin special combustion chambers or pockets alongside the furnace andcommunicating with the main body thereof, whereby the combustion tookplace in a zone slightly removed from the path of the material and thehot gases passed into the furnace proper and around the material beingheated. While this expedient resulted in a slight improvement on theprevious practice, it did not provide absolutely uniform temperaturethroughout the furnace and, in addition, prevented the application of aspecial atmosphere to the treating zone.

I have invented an apparatus for heating, specically, heatingmetallurgical furnaces, which overcomes the objections to the previousprac- 50 tice described above. In accordance with my invention, Iprovide a heating chamber with a plurality of heat-exchange tubesextending thereinto, each tube having a burner adjacent one end and anexhaust at the other. By sup- 55 plying fuel and air to the burners, hotcombustion gases are delivered to the heat-exchange tubes and the latterheat the furnace chamber by convection and radiation. I prefer to employU-shaped or hairpin-loop tubes extending through the walls of thefurnace from opposite sides, although the specific arrangement of thetubes is susceptible of wide variation. In a specic example, the tubesextend through the side walls of the furnace and are disposed above thelevel at which the material being treated is located. The method of myinvention thus provides for the delivery of hot combustion gases in apredetermined direction through a zone adjacent the material beingtreated, and the diversion of the gases to an opposite and substantiallyparallel direction, while confining the heating gases out of contactwith the material being treated at all times. As a further step of theinvention, I prefer to circulate the atmosphere surrounding the tubesand the material being heated to maintain a uniform temperature in allparts of the furnace. The invention is applicable not only to stationaryfurnaces of the continuous or tunnel type, but also to portable furnacesof the cover or bell type, such as shown in my U. S. Patent No.1,952,402.

The accompanying drawings illustrate preferred embodiments and practiceand method of my invention. In the drawings:

Figure 1 is a central longitudinal section through a continuous furnace,in accordance with the invention;

Figure 2 is a sectional view taken substantially along the line II--IIof Figure 1; and

Figure 3 isa transverse sectional view to enlarged scale along the lineIII-III of Figure 2.

Referring now `in detail to the drawings, a furnace I0 comprises ahearth II, side walls I2, a roof I3 and end Walls I4 having entrance anddischarge openings I5 therein. Transverse partition walls I6 having opeirigs therethrough for the passage of material, olvide the furnace intoa preheating zone I'I, a heating zone proper I8, and a soaking zone I9.The walls of the furnace arekcomposed of refractory brick assembled inthe usual structural framework, indicated at 20, the furnace walls beingbuilt up on a foundation 2|.

A plurality of conveyor rolls 22 extend through the side walls I2 andare journaled in suitable bearings 23 mounted exteriorly thereof. Therolls 22 define the so-called roller hearth, and are of the dry or hotshaft type, being composed of heat-resistant alloy capable ofwithstanding continued exposure to the high temperatures involved inmetallurgical operations. Any desired type of drive may be provided forthe rolls 22, as an example of which I have shown the rollers providedwith sprockets 24 adapted` to be actuated by a driving chain (notshown). 'Ihe invention is obviously not limited to .roller hearth"furnaces, and any suitable type of conveyor other than that shown may besubstituted therefor.

For heating the furnace, I provide a plurality of heat-exchange tubes25. In the particular form illustrated, these tubes are U-shaped, orhairpin-like in conformation and extend through each side wall towardthe opposite wall. The

tubes are distributed along the interior of thev furnace and may bemounted therein in any desired manner. In the `illustrated example ofthe invention, the tubes are disposed above the roller hearth on whichthe material traverses the furnace. Each tube is provided with a burner26 having a. connection 21 including a valve 28 to a fuel main 29. Airis supplied to the burner through a connection 30 from a header 3l. Themain 29 and the header 3| extend along both sides of the furnace forconnection to each' burner and are themselves connected to any suitablesource of fuel and air. As will be apparent from the drawings, the twoends of each tube extend outwardly through a side wall of the furnaceadjacent each other. The end not provided with a burner has an exhaustpipe or stack 32 connected thereto for discharging the products ofcombustion to the atmosphere after they have traversed the portion ofthe tube within the furnace.

A plurality of inlet ports 33 is disposed in the side walls I2 of thefurnace adjacent the hearth II to permit the introduction andmaintenance of a predetermined atmosphere within the furnace. While theentrance and discharge doors I permit the leakage of. a certain portionof the furnace atmosphere, the entrance of air from the outside maybeprevented by maintaining in the furnace a pressure slightly above thatof the outer atmosphere.

Circulating fans 34 are mounted in the various zones of the furnace forcausing the continuous movement of the furnace atmosphere between theheat-exchange tubes and the work passing therethrough on the rollerhearth. Each of the fans has a driving motor 35 which is preferablymounted as shown, above the furnace roof on Y suitable supports. By thuscirculating the furnace atmosphere, I am able to maintain asubstantially uniform temperature throughout the space enclosed thereby.If desired, different temperatures maybe maintained in the several zonesof the furnace by'varying the adjustment of the burner valves of theheat-exchange tubes heating that particular portion, and while thecirculation of the atmosphere in any one zone maintains the temperaturethroughout the latter substantially uniform, this does not preclude themaintenance of different temperatures in the various zones, if desired.

A roller conveyor 36 is provided for feeding material toward theentrance door I5. A quenching chamber 3'I is disposed adjacent thedischarge door and provided with cooling means, such as water sprays 38.A discharge conveyor 39 delivers material from the quenching chamber toany desired point.

While the operation of the apparatus described so far will probably beapparent, a brief review thereof will be included here. Assuming thatthe various burner valves have been properly adjusted and the variouszones of the furnace brought up to their proper temperatures, materialsuch as steel sheets to be normalized, is fed into the preheating zoneI1 through the entrance I5 by the conveyor 36. In traversing thepreheating zone, the material`is heated gradually to the desiredtemperature. Ina specic example, the heating zone was 21 ft. long andthe U- shaped heat-exchange tubes were spaced on 18" centers. As thematerial traverses the preheating zone, the heat-exchangetubes radiateheat thereto and the circulation of the furnace atmosphere also conveysheat from the tubes to the material.

As ythe material advances to the heating zone proper I8, it is similarlyheated to the maximum desired temperature. In the aforementionedspecific example, the heating zone was l5 ft. long, with the samespacing of heating tubes. After being brought up to the maximum desiredtemperature, the material passes into the soaking zone, in which it ismaintained at that temperature. 'Ihe soaking zone was 6 ft. long in theexample mentioned. The dimensions of the various zones, of course, aresusceptible of Wide variation, depending on the nature of the operationto be" carried on and the rate of travel of the material thereon. Onemerging from the soaking zone, the material is quenched in a quenchingchamber 31 and is then ready for further nishing operations. Ifquenching is not desired the material may be cooled slowly.

The advantages of the apparatus of my invention have already beenindicated. Among them, is the fact that the combustion gases employedfor heating are maintained out of direct contact with the material beingtreated. It is possible to maintain a substantially uniform temperaturewithin the furnace or the various heating zones thereof. It is` alsopossible to maintain an atmosphere within the furnace different fromthat which would be provided if the combustion gases were dischargeddirectly into the furnace. The U-shaped tubes, furthermore, have an.advantage over the straight tubes anchored at both ends, shown in myprior patent, in that the bent end is free or floating so that expansionand contraction of the tube could not set up any destructive forces inthe furnace walls. The tubes themselves are preferably made ofheat-resistant alloy, to give them a. long life.

Although I have illustrated and described herein but two presentpreferred embodiments and practice of .the apparatus and method of myinvention, it will be apparent that many changes therein may be madewithout departing from the spirit of the linvention or the scope of theappended claims.

I claim:

l. A furnace comprising an elongated heating chamber, having side walls,a roof, and a conveyor for passing material therethrough, heatexchangetubes disposed adjacent the conveyor, said tubes extending throughopposite sides of the chamber alternately, being bent back on themselvesin a horizontal plane and then passing out through the same side wallthrough which they entered.

2. A furnace as defined by claim l characterized by said tubes beingdisposed above the conveyor.

yLEE WILSON.

